The balance of inhibitory and excitatory neurons is essential for a functioning nervous system. Until recently, little was known about the genes involved in regulating the initial formation of these two major classes of neurons. In the past few years, multiple transcription factors have been identified that regulate this process in the developing spinal cord and hindbrain. One essential factor in this process is Ptf1a, a basic-helix-loop-helix (bHLH) transcription factor first identified as a subunit of the pancreatic transcription factor 1 trimeric complex (PTF1). This transcription factor complex is essential for specification of GABAergic/inhibitory interneurons in the dorsal spinal cord, retina, and cerebellum. To uncover the molecular mechanisms controlling the generation of inhibitory versus excitatory interneurons, the following specific aims will be pursued. 1. Investigate the role of autoregulation through the 5'2.5kb enhancer in modulating Ptfla levels in the developing nervous system. Requirement of both halves of the PTF1 sites will be tested by mutation and reporter gene assays by in ovo electroporation in chick. The temporal and spatial expression patterns of this element, and its dependence on Ptfla for activity, will be examined in vivo using a transgenic mouse reporter line. The role of autoregulation in Ptfla function will be investigated by deleting the element in vivo. 2. Identify trans-acting factors regulating Ptf1a in the neural tube through the 3'14kb enhancer. Smaller regions of the 14kb will be tested for dorsal expression in chick to help identify binding sites for candidate factors. These candidates will be tested using overexpression and targeted mutagenesis assays in chick. Furthermore, Ptfla expression will be examined in mice null for the candidates. One such candidate under investigation is NF-kappaB. By elucidating the pathways in which Ptfla is active, this work will advance our understanding of pain disorders, schizophrenia, epilepsy, and congenital cerebellar disorders, and in so doing, suggest therapeutic targets for these diseases as well. Furthermore, the advancement in our understanding of how spinal neurons are formed should accelerate the progress in treating spinal cord trauma.